Sahni Abha, Narra Hema P, Sahni Sanjeev K
Department of Pathology, University of Texas Medical Branch, Galveston, TX, 77555-0609, USA.
Biochem Biophys Rep. 2021 Jan 6;25:100897. doi: 10.1016/j.bbrep.2020.100897. eCollection 2021 Mar.
Cytokines and chemokines trigger complex intracellular signaling through specific receptors to mediate immune cell recruitment and activation at the sites of infection. CX3CL1 (Fractalkine), a membrane-bound chemokine also capable of facilitating intercellular interactions as an adhesion molecule, contributes to host immune responses by virtue of its chemoattractant functions. Published studies have documented increased CX3CL1 expression in target tissues in a murine model of spotted fever rickettsiosis temporally corresponding to infiltration of macrophages and recovery from infection. Because pathogenic rickettsiae primarily target vascular endothelium in the mammalian hosts, we have now determined CX3CL1 mRNA and protein expression in cultured human microvascular endothelial cells (HMECs) infected with . Our findings reveal 15.5 ± 4.0-fold and 12.3 ± 2.3-fold increase in mRNA expression at 3 h and 24 h post-infection, coinciding with higher steady-state levels of the corresponding protein in comparison to uninfected HMECs. Since CX3CL1 is a validated target of microRNA (miR)-424-5p (miR-424) and our earlier findings demonstrated robust down-regulation of miR-424 in -infected HMECs, we further explored the possibility of regulation of CX3CL1 expression during rickettsial infection by miR-424. As expected, infection resulted in 87 ± 5% reduction in miR-424 expression in host HMECs. Interestingly, a miR-424 mimic downregulated -induced expression of CX3CL1, whereas an inhibitor of miR-424 yielded a converse up-regulatory effect, suggesting miR-424-mediated regulation of CX3CL1 during infection. Together, these findings provide the first evidence for the roles of a host microRNA in the regulation of an important bifunctional chemokine governing innate immune responses to pathogenic rickettsiae.
细胞因子和趋化因子通过特定受体触发复杂的细胞内信号传导，以介导免疫细胞在感染部位的募集和激活。CX3CL1（趋化因子 fractalkine）是一种膜结合趋化因子，也能够作为黏附分子促进细胞间相互作用，凭借其趋化功能对宿主免疫反应发挥作用。已发表的研究记录了在斑点热立克次体病小鼠模型的靶组织中，CX3CL1表达增加，这在时间上与巨噬细胞浸润和感染恢复相对应。由于致病性立克次体主要靶向哺乳动物宿主中的血管内皮，我们现在已经确定了感染[此处原文缺失感染的病原体]的培养人微血管内皮细胞（HMECs）中CX3CL1 mRNA和蛋白的表达。我们的研究结果显示，感染后3小时和24小时，mRNA表达分别增加了15.5±4.0倍和12.3±2.3倍，与未感染的HMECs相比，相应蛋白的稳态水平更高。由于CX3CL1是微小RNA（miR）-424-5p（miR-424）的验证靶点，且我们早期的研究结果表明在感染[此处原文缺失感染的病原体]的HMECs中miR-424显著下调，我们进一步探讨了miR-424在立克次体感染期间调节CX3CL1表达的可能性。正如预期的那样，[此处原文缺失感染的病原体]感染导致宿主HMECs中miR-424表达降低了87±5%。有趣的是，miR-424模拟物下调了[此处原文缺失感染的病原体]诱导的CX3CL1表达，而miR-424抑制剂则产生了相反的上调作用，表明在感染期间miR-424介导了对CX3CL1的调节。总之，这些发现首次证明了宿主微小RNA在调节一种重要的双功能趋化因子中的作用，该趋化因子控制着对致病性立克次体的固有免疫反应。
